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Variables And Constant In C Language


Introduction To Variable:-

A variable is a name given to a storage area that our programs can
manipulate. Each variable in C language has a specific type, which determines the size
and layout of the variable's memory, the range of values that can be stored
within that memory, and the set of operations that can be applied to the
variable.
The name of a variable can be composed of letters, digits, and the underscore
character. It must begin with either a letter or an underscore. Upper and
lowercase letters are distinct because C is case-sensitive. Based on the basic
types explained in the previous post, there will be the following basic variable
types:-










Variable Definition in c language:-

A variable definition tells the compiler where and how much storage to create for
the variable.

General Syntax For creating A Variable is

data type_name;

For Multiple Variable Of Same Data type:-

data type_name1,name2,name3..;
For Example :-
int a;
extern int c=6; // declaration of c
static int f;   //static variable declaration
float dd;       //float variable declaration
char w= 'w';    //the variable w has the value of 'w' 
int x=3,y=5,z=9;// definition and initializing

Variable Declaration In "C" language:-

A variable declaration provides assurance to the compiler that there exists a
variable with the given type and name so that the compiler can proceed for
further compilation without requiring the complete detail about the variable. A
variable declaration has its meaning at the time of compilation only, the
compiler needs actual variable declaration at the time of linking the program.

Example Program To Understand Variable In "C":-

#include <stdio.h>
#include<conio.h>
// Variable declaration:
extern int x, y;
extern int z;
extern float d;
int main ()
{
/* variable definition: */
int x, y;
int z;
float d;
/* actual initialization */
x = 40;
y = 10;
z = x + y;
printf("value of z = %d \n", z);
d = 74.0/4.0;
printf("value of f = %f \n", d);
getch();
}

When the above code is compiled and executed, The Output Is :

value of z = 50 
value of f = 18.500000 

Constants In C Language:-

constant is refereed as fixed value and can't be change during its execution
and the fixed values are refereed as LITERALS.
*Constants can be of any of the basic data types like an integer constant  a
 floating constant , a character constant, or a string literal .

Various Literals:

1)Integer Literals:-

An integer literal can be a decimal, octal, or hexadecimal constant. A prefix
specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for
decimal.

The Examples Of Integer Literals Are:-

21 /* Legal */
25u /* Legal */
0xFeL /* Legal */
07 /* Illegal: 8 is not an octal digit */
03UU /* Illegal: cannot repeat a suffix */

Floating-Point Literals:-

A floating-point literal has an integer part, a decimal point, a fractional part, and
an exponent part. You can represent floating point literals either in decimal form
or exponential form.
Examples :-
3.1415989/* Legal */
7159E-5L /* Legal */
90E /* Illegal: incomplete exponent */
10f /* Illegal: no decimal or exponent */
.e55778 /* Illegal: missing integer or fraction */

Character Literals:-

Character literals are enclosed in single quotes, e.g., 'x' can be stored in a
simple variable of char type.
String Literal:-
String literals or constants are enclosed in double quotes "". A string contains
characters that are similar to character literals: plain characters, escape
sequences, and universal characters.
Examples of string Literals:-
"hello, derling"
"hello, \
darling"
"hello, " "d" "arling"

Defining Constants:-

For This Porpous C Language Has Two (2) Methods:
1)Using #define preprocessor
2)Using const keyword

The #define Preprocessor:-

The Syntax For This Method Is-
#define identifier value

Example To Understand #define Preprocessor::

#include <stdio.h>
#define LENGTH 15
#define WIDTH 4
#define NEXTLINE '\n'
int main()
{
int area;
area = LENGTH * WIDTH;
printf("value of area = %d", area);
printf("%c", NEXTLINE);
return 0;
}
THe Output Of This Program Is:

value of area = 602.)The const Method:-

General Syntax Is:-

const type variable = value;
Example Program:-
#include <stdio.h>
int main()
{
const int LENGTH = 15;
const int WIDTH=4;
const char NEXTLINE = '\n';
int area;
area = LENGTH * WIDTH;
printf("value of area : %d", area);
printf("%c", NEXTLINE);
return 0;
}
When the above code is compiled and executed, it produces the following result:
                           value of area = 60

**it is a good programming practice to define constants in CAPITALS.

        THATS ALL ABOUT VARIABLE ND CONSTANTS IN C
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